This invention relates to a data compression technique for binary bit trains derived from the sequential scanning of the adjacent or successive lines of a picture to be coded and transmitted in a facsimile system.
In an uncoded black and white facsimile signal comprising a binary bit train obtained by the constant speed scanning of successive picture lines, the white signal ratio is overwhelmingly predominant in terms of both occurrence and duration, whereby the redundancy rate is very high. Furthermore, there are few changes in the bit patterns between adjacent scanning lines, and the line repetition or redundancy ratio is therefore also quite high. As a result, when a straight black and white facsimile signal is transmitted without coding or modification, as in many of the more simplified prior art devices, the signal redundancy is great which significantly increases the transmission time and cost.